my $url     = URI->new('http://www.safe.nite.go.jp/data/hazkizon/'
    . 'pk_e_kizon_input_second.home_object');

    for my $cas ( '50-00-0', '50-50-1' ) { 

        $mech->get($url);

        if ( $mech->success() ) {
            $mech->form_number(1);
            $mech->select( sel_item1 => 'cas_no' );
            $mech->set_visible( [ text => $cas ] );
            $mech->select( search_meth1 => 'full' );
            $mech->submit();
        }
    }